NEW YORK, Feb 07 (Reuters) -- Drinking a small amount of alcohol each day can protect against stroke, but exposure to cigarette smoke -- including environmental tobacco smoke -- may increase the risk of having a stroke, researchers say.
Cigarette smoking proved a strong predictor of "silent" stroke, that is having stroke without obvious symptoms. Smokers had double the risk of stroke compared with people who never smoked, according to a study conducted at Wake Forest University's Bowman Gray School of Medicine. The results were presented Friday at the American Heart Association's 22nd International Joint Conference on Stroke and Cerebral Circulation.
The researchers studied the brains of 1,805 people, looking for stroke-like brain lesions in people who had no history of a stroke or a transient ischemic attack (TIA) -- a temporary episode which can occur when a blood clot briefly interrupts blood flow to the brain. About one third of those who have a TIA will later have a full-blown stroke. The study authors found that 282 of the subjects had brain lesions that indicated stroke.
While the risk for stroke was greatest among smokers, ex-smokers had a 50% greater risk, and nonsmokers exposed to smoke in their environment had a 20% greater risk of silent stroke.
"From a strictly scientific perspective, I cannot say that passive smoking is associated with these silent lesions," said Dr. George Howard, lead author of the study. "You clearly see a dose-response relationship that increases fairly nicely across the spectrum of exposure to tobacco smoke, beginning with passive smoking."
The Bowman Gray researchers say their findings are consistent with other studies linking environmental smoke exposure and increased thickening of the arteries in the neck that supply blood to the brain. Thickened carotid arteries increase the likelihood of stroke.
Also at the conference, researchers shared new information about the controversial relationship between alcohol and stroke.
Dr. Ralph Sacco, a stroke specialist at Columbia-Presbyterian Medical Center in New York City notes that some studies suggest that excessive drinking increases stroke risk. Other studies have suggested a protective effect from modest consumption.
"The protective effect hasn't been seen in all populations, particularly African Americans," he said, pointing to recent findings of an ongoing investigation. "Studies also have been unclear about the amount of alcohol that is protective."
Sacco and his colleagues examined alcohol consumption during the 12 months that preceded a stroke in 423 people. These findings were compared with year-long alcohol consumption among 793 people with no history of stroke.
After taking into account known stroke risks such as high blood pressure, diabetes, coronary artery disease, and smoking, the researchers focused on the relationship between alcohol intake and stroke risk. In their study, one drink was defined as a standard shot of liquor (1.5 ounces), one beer (12 ounces) or four ounces of wine.
Occasional drinkers -- those who drank less than one drink per month -- had a 62% lower stroke risk than people who never drank. For those who consumed up to two drinks per day, stroke risk was 45% lower compared to nondrinkers. The findings were statistically significant -- that is, they clearly were not merely chance occurrences.
But when alcohol consumption ranged between two and four drinks per day, the association with stroke risk becomes unclear. Drinkers at this level had a 27% lower risk of stroke, but the finding was not statistically significant.
What about heavier drinking? Consumption of more than five drinks daily more than tripled the risk of stroke.
Sacco noted that the stroke-protective effect of light drinking held up for men and women, for different age groups, and for all racial and ethnic groups.
The study also produced evidence suggesting that former heavy drinkers who cut back to light or occasional drinking may enjoy similar protective benefits.
"Drinking heavily in the past doesn't seem to have the same effect as current heavy drinking," Sacco said. "That implies that reforming your habits can have an impact on reducing your stroke risk."
